Biopolymers are finding use as environmentally-friendly alternatives for many common plastics in typical applications, such as in packaging materials and bottling.
One problem with many biopolymers, for instance polylactide, is the poor release from metals when heated above the glass transition temperature (˜50° C. for polylactide). This property is further worsened when heated above the melting temperature of the biopolymer (>150° C. for polylactide). The poor metal sticking release of polylactide leads to difficulties in melt processing, such as release from molds (injection molding, blow molding, thermoforming) and calendering equipment. In the case of calendering, it is not possible to process neat polylactide resin.
Acrylic copolymers have been used as process aids in PVC and polystyrene blends, such as in U.S. patent application Ser. No. 11/053364, however it would not be obvious to use similar processing aids with biopolymers to achieve an improved metal release, as well as an improvement in other properties such as melt strength. In polycarbonate, for example, no significant improvements in melt strength were noted with the use of an acrylic copolymer processing aid.
Surprisingly it has been found that the addition of small levels of certain acrylic copolymers to a biopolymer or biopolymer blend enable biopolymers to be melt processed without the metal release problem. In addition, it was found that the composition of the invention provided improved melt strength, improved draw-down ratio and an improved melt viscosity.